Conventional SIL radar includes a self-injection-locked oscillator (SILO) and an antenna. An oscillation signal generated from the SILO is transmitted from the antenna to an object as a transmitted signal and reflected from the object to the SILO as a reflected signal. The reflected signal received as an injection signal by the antenna is injected into the SILO such that the SILO is locked at a self-injection-locked state to generate a self-injection-locked signal. If the object has a motion relative to the antenna, the transmitted signal generates the Doppler Effect to lead the reflected signal and the injection signal contain phase shifts caused by the relative motion. After the injection signal injects into the SILO, the self-injection-locked signal outputted from the SILO also contains the motion information. Accordingly, the vibration frequency of the relative motion can be detected by demodulating the self-injection-locked signal. Because of non-contact detection of the object movement with high sensitivity, the conventional SILO has been widely used in vital sign measurement.
The sensitivity of the SIL radar is positively related to the center frequency level of the SILO, that is to say, the higher the center frequency of the SILO, the higher sensitivity the SIL radar has. However when increasing the center frequency of the SILO, the propagation loss of the transmitted signal from the antenna and the reflected signal from the object are raised and the available detection area is narrowed. Consequently, the conventional SIL radar having high sensitivity and penetration is difficult to realize.